/*
 * Copyright (C) 2012-2016 Markus Junginger, greenrobot (http://greenrobot.org)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.greenrobot.eventbus;

/**
 * Each subscriber method has a thread mode, which determines in which thread the method is to be
 * called by EventBus. EventBus takes care of threading independently of the posting thread.
 *
 * @see EventBus#register(Object)
 */
public enum ThreadMode {
  /**
   * This is the default. Subscriber will be called directly in the same thread, which is posting
   * the event. Event delivery implies the least overhead because it avoids thread switching
   * completely. Thus, this is the recommended mode for simple tasks that are known to complete in a
   * very short time without requiring the main thread. Event handlers using this mode must return
   * quickly to avoid blocking the posting thread, which may be the main thread.
   */
  POSTING,

  /**
   * On Android, subscriber will be called in Android's main thread (UI thread). If the posting
   * thread is the main thread, subscriber methods will be called directly, blocking the posting
   * thread. Otherwise the event is queued for delivery (non-blocking). Subscribers using this mode
   * must return quickly to avoid blocking the main thread.
   *
   * <p>If not on Android, behaves the same as {@link #POSTING}.
   */
  MAIN,

  /**
   * On Android, subscriber will be called in Android's main thread (UI thread). Different from
   * {@link #MAIN}, the event will always be queued for delivery. This ensures that the post call is
   * non-blocking.
   *
   * <p>If not on Android, behaves the same as {@link #POSTING}.
   */
  MAIN_ORDERED,

  /**
   * On Android, subscriber will be called in a background thread. If posting thread is not the main
   * thread, subscriber methods will be called directly in the posting thread. If the posting thread
   * is the main thread, EventBus uses a single background thread, that will deliver all its events
   * sequentially. Subscribers using this mode should try to return quickly to avoid blocking the
   * background thread.
   *
   * <p>If not on Android, always uses a background thread.
   */
  BACKGROUND,

  /**
   * Subscriber will be called in a separate thread. This is always independent of the posting
   * thread and the main thread. Posting events never wait for subscriber methods using this mode.
   * Subscriber methods should use this mode if their execution might take some time, e.g. for
   * network access. Avoid triggering a large number of long-running asynchronous subscriber methods
   * at the same time to limit the number of concurrent threads. EventBus uses a thread pool to
   * efficiently reuse threads from completed asynchronous subscriber notifications.
   */
  ASYNC
}
